1. Field of the Invention
This invention relates to the field of halogen salts, and particularly to a novel method for producing iodine salts, including, for example, metal iodides, ammonium iodide, and ethylenediamine dihydriodide which are difficult or expensive to make by prior art methods.
2. Description of the Prior Art
Halogen salts have long been used for a myriad of useful purposes, such as analytical reagents, medicines, mordants, photography, single crystals for spectroscopy, feed additives and cloud nucleation. Many pure metals will react directly with halogens to form the corresponding halogen salts. However, the cost involved in obtaining metals in their elemental form have made this process economically impractical. Thus, methods were sought which would permit reaction between metals in the form of metal salts and elemental halogens.
Of the halogens, fluorine, chlorine and bromine are more reactive than iodine. As a consequence, their salts are more easily formed from the elemental state than is possible with iodine. Until recently, several steps were required for the production of many iodide salts. This is particularly true in the case of alkali metal iodides which are commonly produced from ferrous iodide and alkali metal hydroxides in a two step process.
According to one process for producing potassium iodide, potassium hydroxide is reacted with elemental iodine in the presence of water. Both potassium iodide and potassium iodate are produced by this process. In order to remove the undesired potassium iodate from the potassium iodide, the mixture is subjected to fusing at high temperatures. This causes the potassium iodate to thermally decompose before the potassium iodide.
Recently, a method of producing lithium and other alkali metal iodides was set forth in U.S. Pat. No. 3,402,995. This process utilizes an alkali metal hydroxide, elemental iodine and hydrogen sulfide in a water solvent to produce the corresponding alkali metal iodide, sulfur and water. The sulfur is precipitated and must be removed by filtration or other methods before the alkali metal iodide can be isolated by evaporation.
The above described reaction, while more effective than prior art methods, requires removal of the sulfur from the final product. The use of hydrogen sulfide is also undesirable due to its toxicity and flammability. As a consequence, elaborate precautions must be taken in order to protect the personnel involved in making the iodide, as well as to prevent any contamination of the atmosphere.
Also, the method disclosed in the above mentioned patent is stated only to be useful for production of alkali metal iodides. Other iodide salts, including amine iodide salts such as ethylenediamine dihydriodide are not mentioned.
Ethylenediamine dihydriodide, which is widely used as a feed additive and in medicine, can be made by a method which is described in U.S. Pat. No. 2,128,741. The compound is produced by reaction between aqueous solutions of ethylenediamine and hydriotic acid.
The above method for producing ethylenediamine dihydriodide does not include reaction of ethylenediamine with elemental iodine. A separate step, then, is required to make the hydriodic acid from the elemental iodine.